The USB core contains a bug that can show up when a USB-3 host
controller is removed. If the primary (USB-2) hcd structure is
released before the shared (USB-3) hcd, the core will try to do a
double-free of the common bandwidth_mutex.
The problem was described in graphical form by Chung-Geol Kim, who
first reported it:
This happens because hcd_release() frees the bandwidth_mutex whenever
it sees a primary hcd being released (which is not a very good idea
in any case), but in the course of releasing the primary hcd, it
changes the pointers in the shared hcd in such a way that the shared
hcd will appear to be primary when it gets released.
This patch fixes the problem by changing hcd_release() so that it
deallocates the bandwidth_mutex only when the _last_ hcd structure
referencing it is released. The patch also removes an unnecessary
test, so that when an hcd is released, both the shared_hcd and
primary_hcd pointers in the hcd's peer will be cleared.
Signed-off-by: Alan Stern <stern@rowland.harvard.edu> Reported-by: Chung-Geol Kim <chunggeol.kim@samsung.com> Tested-by: Chung-Geol Kim <chunggeol.kim@samsung.com> CC: <stable@vger.kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>